The present invention is directed to the ultrasonic measurement of liquid quantity in a tank, in general, and more particularly to, a method of and apparatus for discriminating among ultrasonic echoes reflected from various objects in the tank containing liquid using wavelet function processing.
Generally, in ultrasonic liquid measurement systems, an ultrasonic transducer is disposed at a tank containing a liquid for measuring the quantity of liquid therein. The ultrasonic transducer is excited to produce ultrasonic pulses into the liquid and receive echoes from the liquid surface and various objects that may be disposed in or a part of the tank. The received echoes are converted into electrical signals by the transducer for down stream electronic signal processing thereof. A metal target or pin is usually disposed at a fixed and predetermined distance from the ultrasonic transducer 40 within the tank so as to compute the speed of the ultrasonic pulse through the liquid in the tank. Briefly, since speed is equal to distance per unit time, then knowing the distance to the target and time over which an ultrasonic pulse is generated and its echo from the target received, speed of the ultrasonic pulse may be calculated. Accordingly, knowing the speed and being able to measure the round trip time from when an ultrasonic pulse is generated until its echo reflected from an object, like the fluid surface, for example, is received, the distance to the reflected object may be calculated. With a prior knowledge of the tank geometry and the distance to the liquid surface, the liquid quantity in the tank may be calculated.
This ultrasonic liquid measurement process seems straightforward. A problem however is being able to discriminate among the echoes reflected from the various objects within the tank in response to the generated ultrasonic pulse. In other words, which received echo is being reflected from which object within the tank. In particular, it is important to determine the difference between an echo reflected by the liquid surface and an echo reflected from an object with a different acoustic property (e.g. impedance) from that of the liquid surface, like the fixed target or tank sides or top, for example. An embodiment of a method and apparatus for discriminating among echoes reflected from various objects within the tank containing liquid will now be described.
In accordance with one aspect of the present invention, a method of discriminating among ultrasonic echoes reflected from various objects in a tank containing liquid comprises the steps of: generating an ultrasonic signal in the tank of liquid; receiving ultrasonic echoes reflected from various objects in the tank including a surface of the liquid in response to the generated ultrasonic signal; converting the received ultrasonic echoes into electrical echo signals representative thereof; sampling the electrical echo signals in time to generate data samples thereof; processing the data samples of each echo using a wavelet function to generate wavelet coefficients thereof in a wavelet domain; and discriminating the ultrasonic echoes reflected from the various objects based on the wavelet coefficients of the echo data samples. In one embodiment, the method step of discriminating includes discriminating an echo reflected from the liquid surface from echoes reflected from other objects based on the wavelet coefficients of the echo data samples of each. In another embodiment, the method step of discriminating includes determining an energy of each ultrasonic echo from the wavelet coefficients thereof; and discriminating the ultrasonic echoes based on the determined energies thereof.
In accordance with another aspect of the present invention, apparatus for discriminating among ultrasonic echoes reflected from various objects in a tank containing liquid comprises: means for exciting the ultrasonic transducer to generate an ultrasonic signal in the tank, the ultrasonic transducer converting the received ultrasonic echoes into electrical echo signals representative thereof; means for sampling and digitizing the electrical echo signals in time to generate digitized data samples thereof; and means for processing the digitized data samples of each echo using a wavelet function to generate wavelet coefficients thereof in a wavelet domain and to discriminate the ultrasonic echoes reflected from the various objects based on the wavelet coefficients of the echo data samples. In one embodiment, the apparatus includes a buffer memory for storing the digitized data samples of each reflected echo, and a programmed digital processor for processing the digitized data samples. The programmed digital processor may include a program for discriminating an echo reflected by the liquid surface from echoes reflected by objects with different acoustic properties from the liquid surface based on the wavelet coefficients of the echo data samples thereof. In another embodiment, the tank may be an aircraft fuel tank and the liquid comprising aircraft fuel.